1. Field of the Invention
The present invention relates to an imaging apparatus such a digital camera, and in particular, relates to a mirror and shutter drive control mechanism in an imaging apparatus allowing a user to select between two types of view modes: optical view mode in which the object is viewed through an optical viewfinder before photographing, and live view mode in which an electronic object image captured by an image sensor is viewed in real-time on a display monitor before photographing.
2. Description of the Related Art
In addition to a conventional object viewing function (optical view mode) using an optical viewfinder, SLR digital cameras having a ‘live view mode’, in which an electronic object image captured by an image sensor is viewed in real-time on a display monitor such as an LCD before photographing, are known in the art. In the live view mode, the quick-return mirror (hereinafter referred simply to as the mirror) is held in the retracted position (mirror-up position) in which the quick-return mirror is retracted from a photographing optical path when the object is viewed before photographing, which is different from a viewing state in the optical view mode, in which the object is viewed through an optical viewfinder before photographing. Therefore, when a photographing operation is performed in the live view mode, the mirror drive operation and the shutter drive operation need to be controlled in a different manner from those in optical view mode (normal exposure mode).
In the SLR camera disclosed in Japanese Patent No. 3,153,482, a mirror up/down operation, a shutter charge operation, a diaphragm control operation and other operations are performed by rotations of cam-incorporated gears driven by a single motor. Although Japanese Patent No. 3,153,482 is for a camera using silver film, a live view mode operational sequence that allows a photographing operation to be carried out (referred hereinafter as “live-view mode photography operational-sequence”) can be designed and configured in an SLR digital camera using a drive mechanism including such cam-incorporated gears.
In the SLR digital camera disclosed in Non-Patent Document 1 (pages 202 and 203 in “Asahi Camera” (a Japanese monthly photographic magazine published by Asahi Shimbun Publications Inc., print edition, August 2008), another image sensor (live-view image sensor) used exclusively for capturing the object image in the live view mode, independently of an image sensor used for taking pictures, is installed in a viewfinder optical system so that a quasi-live view operation can be performed using the live-view image sensor in the viewfinder optical system.
In SLR cameras having two independent drive sources for a mirror drive mechanism and a shutter drive mechanism, respectively, like in the case of the SLR camera disclosed in Non-Patent Document 2 (pages 230 and 231 in “Asahi Camera” (a Japanese monthly photographic magazine published by Asahi Shimbun Publications Inc., print edition, January 2008), the photographing operation in the live view mode can make the shutter drive mechanism perform a shutter charge operation while making the mirror drive mechanism hold a mirror-up state (i.e., hold the mirror at the retracted state thereof), and is thus easy to control compared with that performed in the SLR camera in which the mirror and the shutter are driven by a common drive source.
In the type of SLR camera disclosed in Japanese Patent No. 3,153,482 in which a mirror drive operation, a shutter charge operation and a diaphragm control operation are performed by a single drive source, miniaturization and weight reduction can be achieved by the sharing of the drive source. On the other hand, if a digital camera having this type of drive mechanism is designed and configured to perform a live-view mode photography operational-sequence simply by using the drive mechanism that controls a normal photography operational-sequence (i.e., an optical-view mode photography operational-sequence), it has been proven that unnecessary operations, except the actuation of the shutter, e.g., the mirror up/down operation and the diaphragm full-opening operation, are performed every time a photographing operation is performed during the live view mode. Hence, the usability of the camera is adversely influenced since the image on the monitor momentarily appears black upon rise and fall of the mirror in the live view mode. In addition, also from the viewpoint of load reduction and improvement in operational speed, it is desirable that such unnecessary mechanical operations not occur.
In the SLR camera disclosed in Non-Patent Document 1, an electronic image captured by an image sensor different from the image sensor used at a time of exposure is viewed on a display monitor before photographing, and accordingly, this view mode cannot be considered to be a live view mode in the strict sense, as there is a possibility of the image displayed on the monitor not precisely coinciding with the image taken at a time of exposure. Additionally, installation space for an image sensor needs to be secured in the viewfinder, which becomes an obstacle for miniaturization of the camera and causes an increase in production cost.
In the case of employing a structure disclosed in Non-Patent Document 2, although the mirror up/down operation can be prevented from occurring during a photographing operation that is performed during live view mode, the mirror drive system and the shutter drive system are provided with two independent drive sources, respectively, which causes an increase in size, an increase in weight of the camera, and also an increase in production cost.